745. CD4-T Cell Responses Mediated by IFNγ and Perforin Eliminate Adenoviral-Mediated Transgene Expression from the CNS of Mice by Cytolytic and Non-Cytolytic Mechanisms

Abstract

Gene therapy approaches using first generation adenoviral vectors (RAds) can achieve long-term transgene expression in the brain, and therapeutic effects in animal models of brain tumors and neurodegeneration. However, long term expression and vectors' efficiency can be limited by immune responses, characterized by inflammation in the brain and the eventual elimination of transgene expression. Injection of first generation RAds into the striatum followed by peripheral immunization has allowed us to determine the cellular and molecular mechanisms by which the adaptive immune response regulates transgene expression in the CNS. Our experiments provided the following results: (1) systemic immunization against RAd reduced transgene expression by 30 days post-immunization; (2) the time course of entry of lymphocytes into the brain is as follows: first, CD4+, followed by CD45+ and F4/80+, and lastly, CD8+ T cells; (3) lymphocytes and macrophages contacted and phagocytosed transduced cells; (4) transgene expression persisted in the CNS of Rag1(|[minus]|/|[minus]|), CD4(|[minus]|/|[minus]|), IFN|[gamma]|(|[minus]|/|[minus]|) and perforin(|[minus]|/|[minus]|) animals; and (5) even in the absence of transgene expression, we could detect the presence of RAd genomes by quantitative TaqMan PCR. In summary, our data suggest the existence of a CD4-T cell response mediated by IFN|[gamma]| and potentially perforin that eliminates transgene expressing cells from the CNS. The continued presence of viral vector genomes, suggests the presence of non-cytolytic mechanisms as well. The balance of cytotoxic, and non-cytotoxic mechanisms is currently being investigated further.